The production of electrical printed circuit boards for computers, and the like, has been substantially standardized. The components are placed and soldered successively. In many cases, the circuit boards must pass through a solder flow a number of times, one passage before the other, before completion of the circuit boards. Various sections or components of the circuit boards, such as gold connector fingers and tracers, must be masked off so as to protect them from the solder flow.
In accordance with the usual practice in the industry, either liquid rubber, glass or poly tapes are applied to sections or components on the circuit board to mask off the solder flow. The liquid rubber must be cured before the soldering process can begin.
When the circuit board is ready for processing, i.e., soldering, a conveyor may carry the circuit board to a water-soluble flux where soldering is effected. On the other hand, the circuit board may be soldered in a rosin. After all solderings are complete, the rubber, poly, or glass tapes must be removed without damaging the gold contacts or other components. After removing the masking, the circuit boards pass to a final wash process in the case where a water-soluble flux has been used for removing the flux. When rosin is employed, the circuit board after soldering goes to a degrease, at temperatures from 50.degree. F. to 380.degree. F.
The known process employing water-soluble flux has two particular problems in respect to masking. First, the rubber masking can seep into small holes in areas where its removal is difficult to effect. Second, glass and other tapes leave a residue which interferes with the effective use of the circuit boards. As a result, a solvent cleaning step must be used to effect removal of the residues, in addition to the washing process.
It has been known to provide a masking comprising gums and salts, by applying wetted adhesive to the circuit boards. These masks, however, have not been successful, particularly because of leaving residues on the circuit board components which make it unsatisfactory. Such residues remain, even though the mask is washed from the circuit boards by solubilizing of the mask. Further, the required wetting of the adhesive inherently places moisture between the masking and circuit components, resulting in unsatisfactory soldering conditions. Additional problems encountered in using wetted adhesive, include a requirement for additional personnel and a period of 15 to 30 minutes for drying causing a slow operation and increased costs.
It is important that the masking not contaminate the circuit board components before and after removal, and that the masking be water-soluble, non-toxic, and biodegradable. Further, the masking material should be readily removable in existing washing operations for circuit boards.
The principal object of the invention is the provision of an improved masking for use in soldering operations, and particularly for use in the manufacture of electrical printed circuit boards and the like.
A further object of this invention is the provision of an improved masking which is water-soluble, non-toxic and biodegradable.
A still further object of the invention is the provision of an improved masking which can withstand the heat conditions inherent in the manufacture of the electrical printed circuit boards while maintaining its water-solubility and biodegradability.
Another object of the invention is the provision of a masking which can be readily applied during the manufacture of electrical printed circuit boards, and removed from the circuit components without leaving any residue upon the components.
Still further objects and advantages of the invention will become apparent by reference to the following description: